The long-term objectives of this proposal are to describe age-related changes in sensitivity to auditory transients during the course of normal development, and to characterize the mechanisms underlying these changes. The proposed research has two major objectives. The first is to describe the temporal characteristics of short-term integration in young infants. The second is to examine intensity coding for both transients and longer- duration stimuli during infancy and early childhood. Three proposed studies will 1) determine the critical interval for efficient spectral summation of brief multiple-component tones; 2) examine the time course of short-term temporal summation in quiet and noise backgrounds; and 3) describe the shape of the hypothetical temporal window in young infants. Two additional studies will examine the role of efficient spectral summation in intensity discrimination of noise bursts, and describe developmental changes in intensity discrimination of brief and longer- duration tones. These experiments will employ either a go/no-go visually reinforced operant technique or a 2-alternative directional headturn procedure. Subjects will be infants and children ranging from 7 months to 5 years of age; adult subjects will also be tested for comparison. Results of these studies should further our understanding of normal auditory system development, and may also contribute to our knowledge of the organization of auditory function in adults. An understanding of the mechanisms involved in sensitivity to transients may also contribute to our understanding of processes involved in the perception of speech, and may be of particular relevance in clinical applications, since procedures most widely used in hearing tests of young infants (e.g. Auditory Brainstem Response) require the use of very brief auditory stimuli.